hibernate-mapping

I have a table that has foreign key of another table (many to one relationship) but i want it to be nullable. Something like this: public class SubType() { @Id @GeneratedValue(generator = "system-uuid") @GenericGenerator(name = "system-uuid", strategy = "uuid") private String id; } public class TopUp { @Column(nullable = true) @ManyToOne(optional = false, fetch = FetchType.LAZY) private SubType subType; } But @Column(nullable = true) throws the NullPointerException and says subtype can not be null. Is there any way to get the ManyToOne accept null? You need to set: @ManyToOne(optional = true,

consider table sales (id, seller_id, amount, date) and here is a view that is generated from sales using query SELECT seller_id, SUM(amount) FROM sales GROUP BY seller_id total_sales (seller_id, amount) I want to make an entity for total sales but without the view on the sql side. This entity will be constructed from a query. The closest thing I found is this , but I could not make it work. Even if I define the loader, hibernate looks for the entity's table and gives an error if it cannot find it. If I create the table it does not load the entity from the named query I defined, Hibernate

As usual Java enum types have corresponding codes and name description. And Java classes that contain such fields, contain them as Enum: public enum MyEnum{ SOMEINSTANCE(1, "test1"), SOMEINSTANCE(2, "test2"); private final int code; private final String name; private MyEnum(int code, String name){ this.code = code; this.name = name; } ... helper getter for code and name } @Entity puclic class EnumHolder{ private MyEnum myEnum; } I'm a newbie to JPA, but I wish to have the ' myEnums ' table, looked like: code int not null, name varchar(50) not null) And in my enumHolder table I want to have the